The PS-OW is a diaphragmactuated electric control operated by pressure or vacuum. Pressure or suction applied to the diaphragm moves it against the adjustable spring and operating mechanism. When pressure or suction exceeds the spring setting, the mercury switch closes or opens. Three adjustable spring pressure ranges are available and springs are easily interchanged in the field. Switches are used to assure proper operation of combustion equipment by proving adequate fuel and air pressures and flows. FEATURES Range 0.2'' to 27'' W.C. with same switch - Change in spring only Requires only screwdriver for field pressure adjustments Pressure connections on bottom to eliminate condensation problems Large pressure chambers absorb pulsations - eliminate nuisance shutdowns Simple installation 3-point mounting brackets and bubble level included Switch position visible through window Switch assembly can be replaced without disconnecting All switches factory tested before shipment